1. Field of the invention
The present invention concerns a system for interconnecting orthogonally disposed printed circuit boards forming part of respective first and second stacks. It also concerns switching networks using cascaded selection stages employing one or more such interconnecting systems, such switching networks being employed in telecommunication networks and in particular in telephone networks used to transmit digital data at high bit rates, for example 45 Mbit/s.
2. Description of the prior art
One method of interconnecting orthoganally disposed printed circuit boards is described in French Pat. No. 2 109 246.
It is used to interconnect successive selection stages of switching networks, in particular of networks with three cascaded selection stages each defined by a stack of appropriately equipped printed circuit boards.
According to this document, for the purpose of interconnecting orthogonolly disposed printed circuit boards forming parts of stacks defining two successive selection stages in a switching network, there is provision for placing the inputs and outputs of each board on a common edge in the respective stack. These edges in the two stacks are in face-to-face relationship and the boards of one stack are disposed orthogonally to the boards in the other stack. The selection stages are interconnected by a simple plug-in action by having contact members connected to the various inputs and outputs of each of the boards in the two stacks cooperate with each other. These contact members are hermaphroditic members or may be male contact members in the case of the boards in one stack and female contact members in the case of the boards in the other stack. This interconnection method makes it possible to eliminate all wiring between the boards in the two stacks.
In the specific embodiments described in this prior art document the contact members are mounted in pairs and those in each pair are on opposite sides of the board concerned. Interconnecting successive selection stages using this interconnection method necessitates adopting the same modular spacing between boards and contact members. Thus to the degree that the thickness of the boards is less than the distance between two contact members on the same side, an appropriate make-up member is attached to one side of the boards. As applied to printed circuit boards this technique is highly impractical and makes it doubtful whether this interconnection method can be implemented on an industrial basis. It would also seem that the electrical connections made and the mechanical strength of the connections at the level of the contact members are somewhat unreliable.
According to the same document, in a switching network with three cascaded selection stages using this interconnection method between two successive stages, the boards of the two terminal selection stages are disposed parallel to each other and perpendicular to the boards of the intermediate selection stage. The boards of the two terminal stages are advantageously L-shaped so as to carry on one and the same edge the contact members for connection to the boards of the intermediate stage and connectors for connecting the boards of the terminal stages with the input circuits (terminals) and the output circuits (junctors) to be connected selectively to each other. In this way the connectors are on the outside of the intermediate selection stage and make it possible to utilize a "backplane" type distribution frame.
An object of the present invention is to provide a method of interconnecting orthogonal boards that totally eliminates any wiring between the boards and further makes it possible simultaneously to achieve distribution of signals to the various boards, all this compatibly with known requirements in terms of the reliability of the connections made and industrial manufacture of the interconnecting system and the switching networks using it.